Broomer5 did a good write up about the process that was used when he switched over his tanks... if he happens upon this thread hopefully he will post it.
I happened upon this thread NaCL-Man
novafreakjj - Personally I would not try and remove the crushed coral without first removing everything from the tank.
It will foul the water - and foul water leads to fish/inverts stress.
Extreme stress may lead to disease or death.
It may sound like a do-able thing, and I'm sure others have done it this way .... but in my opinion, starting fresh is the best in your case. Best for your critters, and in the long run better for the health of the tank.
I changed out a 55 gallon reef tank with very nasty crushed coral substrate .... to a 75 gallon tank with DSB in one weekend.
The 75 was going in the same location in the room as the 55 - so you can imagine my situation. I had to tear one down - and set the other up in it's place.
There are a lot of details that need to be covered here - but the one key is taking care of the water. If you take care of the water - the water can take care of the fish/inverts and bacteria.
The other key is whether you have a lot of live rock, or you are using some other filter. Keeping the filter running and the rock in warm moving water is also very important.
I bought several inexpensive rubbermaid type plastic containers, rinsed them out first with tapwater and dried them.
Get as many containers as you need ( gallons ) but only fill them up half way or so. They tend to bow out some - and it's better to have two 30's filled halfway - than one 30 filled to the rim.
All of the aragonite sand was purchased - buy more than you think you'll need. Spare heaters/powerheads are required as well. If you plan to do a water change during the swap - have your mixed aerated saltwater ready the night before.
Basically you siphon off about half the tank water to the plastic containers. Place a heater/powerhead in each container.
Keep the water moving.
Keep the water warm - same temp as tank.
If you have a hang on filter - hang it on the container and turn it on.
You want to keep ALL FILTER MEDIA wet, warm and running.
Remove some of the live rock and place in the containers.
Remove some of your corals - gently place them in these containers.
Once you get all out of the tank - it's easy to net your fish at this point.
Net them - and place in the container. No need to acclimate them - they are going into the same water.
Siphon off some more of the tank water into these rubbermaid holding containers.
Leave an inch or so of water in the tank, so you don't suck up any substrate or crud. Gather up all your crawling inverts - and yep ~ you got it - place them in the containers.
Siphon off the rest of the tank water and discard to a bucket/drain.
Now comes the nasty part - but it goes fast if you keep at it.
Scoop out all of the nasty crushed coral and throw it away. If you want to keep some for bacterial seeding of your new sandbed - you can place some of this cc in pantyhose or filter media bag and tie it off. Toss this in the container with your container of warm moving water.
Keep scooping out all of the CC until it's gone.
Rinse out the tank - it will smell pretty bad if it's been up awhile.
Just rinse all the crap out - and if you want - now's a good time to do some inner tank wall scraping/cleaning.
No detergents - no soap - no bleach - just warm tapwater, plastic scraper and rinse out well.
Check your temperature in your container often. What you want is for this container(s) to be identical in temp/salinity that you tank was.
Place the tank back on the stand.
Lay down your sandbed to desired depth.
Normally 4-6 inches of sugar size aragonite is good if you want a deep sandbed. Less sand if you prefer a shallow sandbed. Up to you.
Place a clean glass bowl on the sandbed - and "pump" some of the water from these holding containers back into this bowl. If you don't have a spare pump - pour water in slowly with a clean plastic or glass pitcher.
Doing it this way will keep the new sandbed from getting all stirred up. It will help a lot.
Keep adding saltwater until you have it about a 1/3rd full.
Now add some of your live rock back. Start with the base and build up your stack.
Add some more saltwater.
Add some more rock.
Continue doing this - but leave a little room at top - in other words - don't add all the water back until you get everything back in the tank.
Add your corals/inverts.
Top off the tank with rest of saltwater - or add a little new mixed.
Power up your filters, equipment, powerheads, heaters and get the water moving again in the tank.
Net your fish and add them back.
Some folks will acclimate them back into the tank.
If the water is same, and was kept at same temp - you should be okay. I was.
Gather up the last few hermits, snails or whatever else is left in the containers and get them back into the tank too.
Clean up your mess.
Now ....... the disclaimer.
It took me two days to do this. The reason being, I did a rather large water change at this point as well.
I kept the fish and corals in these containers "overnight" with heater/powerhead in each vessel. I had three containers - all going at once.
I don't recommend doing a large water change if you have delicate species.
The next day the water was much clearer - and I had no hesitation moving forward with the rest of the procedure.
My fish, crawling inverts and corals ALL made this transition without a single loss.
If you just set up these rubbermaid or sterilite plastic containers - and keep the water warm and moving - just as you would any other tank - the chances of losing your fish/inverts, corals and BACTERIA are low.
If you do NOT keep the water at temp and moving/circulated - you risk losing much.
It's not difficult - it just takes time and a great deal of attention to the details.
BTW - this is just ONE way to make the swap.
It worked for me. It may not be the best - nor is it the worst.
I just moved my 75 reef tank from upstairs to downstairs 2 weeks ago, using this exact same method. Once again - no cloudy tank, new sandbed and most important - no losses.
Good luck however you choose to do it novafreakjj